Pack rendered images into .blend?
If I am correct, you want to automatically save the rendered result so if Blender crashes you have the last known output.  Using composition you can save the output as follows:



This image, by default, will be called Image0001.png in your chosen path. If you really really really wanted to pack it in the Blender file I suppose you could create a non-rendered object that takes that image and then it should also be stored (not tested). However, I think just the automatic saving is probably what you are after.